| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel material for heavy heat input welding which exhibits excellent toughness in a welding-heat-affected zone, even when subjected to heavy heat input welding with a welding heat input of more than 300 kJ/cm.SOLUTION: A steel material for heavy heat input welding comprises, by mass%, prescribed amounts of C, Si, Mn, P, S, Al and Nb and further comprises 0.004-0.030% Ti, 0.0003-0.0030% B, 0.0035-0.0070% N, 0.0005-0.0030% Ca, ≤0.0040% O and the balance being Fe and unavoidable impurities, while satisfying following relation (1): 0<(Ca-(0.18+130×Ca)×O)/1.25/S≤0.40, wherein Ca, O and S represent the contents (mass%) of corresponding components. When the steel material for heavy heat input welding is subjected to heavy heat input welding with a welding heat input of >300 kJ/cm, the grain size of intergranular ferrite is ≤50 μm in a structure of a welding-heat-affected zone in the vicinity of a bond. |
